ADVANCES IN IMAGING TECHNOLOGY
Medical Imaging is the foundation of modern evidence based practice of Medicine. It started more than 100 years ago with discovery of x rays by Wilhelm Conrad Röntgen in 1895. X rays are still relevant in contemporary medical imaging. Discovery of solid state x ray flat panel detector not only resulted into digitization of x ray shadow of body part but also resulted into better contrast and spatial resolution at much lower radiation dose. Presently direct digital radiography with Caesium iodide flat panel detector produce highest quality x ray image with lowest radiation. The advancement has happened not only in x ray production and image generation but also in post processing of acquired images. Algorithms are developed to edit out bones from the images, stitching of images to get larger field of view and tomographic imaging. Rotation of x ray tube and detector assembly around the subject of interest and post processing of detected x-ray data gave birth to new technology called Cone Beam Computed Tomography (CBCT). This technology enables us to get CT scan like brain images in Neuro angiography suites. This technology is already popular in dental radiography.
Computed Tomography (CT scan) is an imaging modality based on x ray. It provides sectional images. Many advancements have been made to this modality. Ultra fast Multidetector CT scanning is enabling us to take entire volume in one go. This has resulted into DSA like neuroangiography at 3 frames per second. It has enabled single rotation cardiac imaging without the need of beta blocker or breath hold. Dual energy CT scanning can give virtual non-contrast image (thus alleviating the need of precontrast scanning), enable us to get postcontrast scanning at low dose of contrast, gives insight into composition of renal stone, Bone removal from acquired images for better CT angiograms and detection of bone bruises by detecting significantly higher fluid attenuation in areas of bone in bone subtracted images. Spectral CT scanning goes further by providing effective atomic number of region of interest within the image. Change in image reconstruction algorithm from conventional to iterative reconstruction algorithm significantly reduced radiation dose for equivalent quality of images. Significant advancements has been made in post processing of images. Cinematic rendering of 3D volume dataset brings life like images. CT perfusion imaging has role in stroke in predicting outcome, in oncology to differentiate benign versus malignant and in evaluating response to therapy. CT perfusion imaging is also extended to cardiac imaging to look for ischemic areas in resting and stress conditions. CT scanner is miniaturized to make it portable. Now bedside and intraoperative CT scanning is also possible.
Ultrasound is the most accessible modality without using any ionizing radiation. It has gone from 2 dimentional sectional images to 3D static and dynamic imaging. Advancement in image acquisition and post processing resulted in high frame rate of dynamic 3D (4D) images. New post processing technique like “silhouette” (proprietary, GE healthcare) has brought photo realistic fetal imaging. Automation of measurements of Nuchal translucency and biometric parameters, is made possible by pattern recognition algorithms. New generations of ultrasound equipments have appeared. These has tremendously increased the frame rate by complete change in the way images are acquired. In this context two companies deserve special mention—Supersonic imagine and Zonare. The ultrafast imaging of supersonic imagine brought real time shear wave elastography (evaluation of tissue elasticity for detection of cirrhosis, malignancy etc. Simultaneous display of grey scale images, color Doppler flow mapping and flow waveforms in real time. Retrospective placement of volume box for flow waveform evaluation is also possible. Zonare’s radically new approach to image acquisition technique called “zone-sonography” brought 10 times faster frame rate, all pixel in frame always being in focus (dynamic pixel focussing) and sound speed compensation for better resolution.
MRI (magnetic resonance imaging) is the most recent imaging modality but it the most versatile and has opened multiple types of image contrast thus producing better tissue characterization. Tremendous development has happened in MRI technology in recent years. New pulse sequences are being developed and the possibilities are endless. Not only this, advancements are also made to make it affordable and are moving towards cryogen free / less cryogen requiring magnet. Coil design, signal handling and post processing of raw data, are also improving. Esaote’s “G-scan” and Paramed medical systems’ ‘MR open” made MRI in weight bearing standing postion possible. Not only these made MRI comfortable but also made dynamic and functional MRI possible. Ultra high field MRI (upto 7 Tesla)are also developed. These have special application in neuroimaging. Toshiba introduced its Ultrashort Echo Time (UTE) sequence for dedicated pulmonary MRI and MRI for pathologies within ligaments and tendons (these are otherwise dark in conventional MRI). MR elastography evaluates tissue elasticity, which is altered in pathological states. . SWeep Imaging with Fourier Transform (SWIFT) imaging is helpful in dental imaging. It detects caries, tooth canal abnormalities and other pathologies. Molecular MR imaging is defined as “probes used to visualize, characterize, and measure biological processes in living systems. MR spectroscopy using proton, phosphorus and sodium gives insight about different metabolites High field MRI requires helium which is fast depleting and very costly. “Freelium” technology from GE requires only 20 litres of helium against thousands of litres of helium.